Mail processing systems, such as, for example, a mailing machine, inserter, and the like, often include different modules that automate the processes of producing mail pieces. A typical mail processing system includes a variety of different modules or sub-systems each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. In a mailing machine, such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering/printing module, i.e., applying evidence of postage to the mail piece. In an inserter, such modules could include one or more feeders and collators, an envelope stuffing module, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering/printing module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mail processing system is, of course, particular to the needs of the user.
Modern mail processing systems utilize digital printing techniques for producing images on a mail piece. Conventional digital printing techniques include bubble jet and ink jet, each of which produces an image in a dot matrix pattern. With digital printing, individual print head elements (such as resistors or piezoelectric elements) are selectively electronically stimulated to expel drops of ink from a reservoir onto a substrate, e.g., a mail piece. In either case, by controlling the timing of energizing of the individual print head elements in conjunction with the relative movement between the print head and the mail piece, a dot matrix pattern is produced in the visual form of the desired image. In the case of mail processing systems, the image may be, for example, an indicium that evidences payment of postage or advertisements printed on the outside of a mail piece.
Digital printing technology has significant advantages when used in a mail handling apparatus as compared to older technology that utilized either a flat platen or a rotary drum to imprint information, such as, for example, address information or an indicium, on mail pieces. For example, if some variable image data needs to be changed, it can easily be done through the installation of new or upgraded software versus having to replace the entire printing module, since the flat platen and drum are typically not separately removable. Moreover, greater printing speeds can be obtained as compared to conventional mechanical printing systems. However, the use of a digital print head in a mailing system presents other issues that must be taken into consideration. For example, for the ink jet nozzles of an ink jet printer to properly deposit ink on the surface of the receiving medium, it is critical that a small predetermined gap be maintained between the exit plane of the nozzles and the surface of the receiving medium, typically in the order of 0.02 to 0.08 inches (0.5 to 2.0 mm). This gap is necessary to achieve acceptable image quality, since too small a gap causes scuffing of the print head and to large a gap results in inaccurate dot placement, with either situation resulting in a deteriorated print image. Thus, in the mail handling environment, it becomes necessary to maintain this critical gap between the exit plane of the ink jet nozzles and the upper surface of the mail pieces being conveyed through the mailing machine.
To accomplish this, the mail pieces, such as, for example, envelopes, postcards, flats, and the like, must be conveyed with the front panels on which the information is printed lying in a fixed registration plane, which is disposed beneath the exit plane of the nozzles a distance equal to the aforementioned gap. This arrangement is referred to hereinafter as top registration. To accomplish this top registration, a biasing force is applied to the back panel of the mail piece such that the front panel maintains light contact with a registration plate. This contact slightly compresses and flattens out the mail piece, thereby establishing its surface at the ideal gap distance from the print head nozzles. An opening is provided in the registration plate, above which the print head is located such that the print head can print on the mail piece as it passes the opening in the registration plate.
There are problems, however, with the conventional top registration transports in mail processing systems. Conventional registration plates maintain the desired gap when printing on thin or constant thickness media in which the print surface is flat. When printing on variable thickness media, however, such as mail pieces that are filled with different amount of inserts that tend to make the mail pieces “puffy” or have distorted top surfaces, it is difficult for conventional registration plates to maintain the desired gap due to the variations in the surface profile of the mail piece. This problem is exacerbated when the printing zones are wide, which requires the use of wide print nozzle arrays to perform the printing, as the openings in the registration plate must also be larger to accommodate the print nozzle arrays. These larger openings do not provide support for the mail pieces, resulting in large variations in the surface profile of many mail pieces as they pass under the print nozzles. This results in variations in the spacing between the print nozzles and the surface of the mail piece, which in turn causes poor print quality. In addition, the variations in the surface profile can result in a portion of the mail piece surface protruding into the opening and contacting the print nozzles as it is transported past the print head, which can cause smearing of the ink and potentially damage the print nozzles. Additionally, if there is a jam of the mail pieces being transported in the printing area, there is a much greater chance that a mail piece will be forced into the opening, because of the larger openings, and contact the print nozzles.
Thus, there exists a need for a top registration device for a mail processing system that utilizes wide print nozzle arrays that reduces the problems associated with printing on variable thickness media.